So I wear a lot of vintage. I don't, however, wear the underpinnings that would give me a proper vintage shape. There are a couple of reasons for this.
The first is just plain luck. I happen to be blessed with a figure that's well-suited for vintage: I have narrow shoulders, an average-sized bust and a small waist. My big hips are easily hidden in the swish of a full skirt. My figure is pretty much what the New Look designers had in mind, and I don't need to alter my shape to match their ideal. If I wanted to wear '20s or '30s styles it would be a different story, but I'm pretty well built for the '50s and early '60s.
The main reason, though, is that I'm kind of uncomfortable with the the societal underpinnings of vintage underpinnings. Shapewear is restrictive, both physically and phsychologically: it's meant to constrict your body and your movement. It's meant to mold you into something that nature hasn't intended you to be, into a shape that's in keeping with whatever fashion currently dictates.
The history of shapewear, from the earliest corsets onward, is a history of women being molded to suit fashion, contorting their bodies to match one another. A woman born at the end of the Victorian era would have seen a half a dozen 'ideal' shapes come and go in her lifetime, each with its own set of underwear meant to mold her body into that new shape.
Even today, different body types come in and out of style. It's just that nowadays, if your body doesn't suit the current fashion, you just kind of resign yourself to not finding anything cute in the stores until fashion changes. I don't know that this is a better option-- in an ideal world, fashion would embrace a wider range of body types. But this obviously isn't an ideal world.
I'm not saying I judge or look down on women who *do* choose to embrace shapewear, vintage or modern. I'm just saying that I, personally, am uncomfortable with the implications of it, and choose not to wear it myself. The fact that it's a choice I can make is awesome, and one of the many reasons I'm glad to be a vintage-wearing girl in the 21st century.